1. Field of the Invention
This application relates to pulley drives and especially to pulleys constructed of a pair of flanges with at least one of the flanges axially movable with respect to the other. Such pulleys find use in variable pulley transmissions and especially those referred to as continuously variable transmissions (CVT). The pulleys in a CVT are connected by means of drive belts, chainbelts or the like.
2. Background Information
Variable pulley transmissions have been used for some time for transferring torque from an input or drive shaft to an output or driven shaft. In these transmissions, a first pulley constructed of a pair of flanges is mounted on the input shaft such that at least one of its flanges is axially movable with respect to its other flange. A second, similarly constructed and adjustable pulley, is mounted on the output shaft. A flexible belt connects the two pulleys to transfer torque therebetween when the input shaft is driven. As the effective diameter of one pulley is changed by flange movement along the shaft axis and, simultaneously, the effective diameter of the other pulley is changed by flange movement in the opposite direction, the speed ratio between the input and output is adjusted in a smooth, continuous manner. Mechanical or hydraulic means and/or combinations of the two means are usually provided for initiating the drive ratio changes. The prior art is replete with such arrangements.
In the prior art, the axially movable flange of each pulley or a hub of such flange may be provided with an internal keyway to receive a key fitting in a keyway in the respective shaft. The key and keyway provide the driving connection between flange and shaft while permitting axial movement of at least one of the flanges. Keyways are machined in the shafts and flanges, an expensive procedure, and lubrication of the key-keyaway connection is a necessity to prevent galling and/or binding, although such lubrication is difficult at times. In the absence of proper lubrication, the key may bind in the keyways, flange movement would be inhibited and drive ratio changes impeded. Loading on an unlubricated key becomes excessive due to the mass of the pulley rotating at relatively high speeds, which leads to premature failure of the transmission.
Another form of movable flange-shaft connection is a ball and spline arrangement, which uses a plurality of balls functioning as anti-friction elements with a spline. The ball-spline connection is located internally of the flange and/or its hub. This type of connection is expensive and requires continuous lubrication to ensure its continued performance. Loading on an unlubricated spline of the ball-spline connection can also become excessive, leading to premature failure of the transmission.
Instead of movable flange-shaft connections as above described. Bessette, in U.S. Pat. No. 3,868,862 teaches the use of a pivotably connected link or links between the movable flange and the drive member. In one embodiment, a single link is circumferentially arranged with respect to the flange and drive member. Another embodiment illustrates three spaced links angularly arranged with respect to the flange and drive member. In both embodiments, the links must be rigid or stiff and must be provided with pivoting joints, which are universal joints in the case of the second embodiment. These joints must be constantly lubricated to operate properly. The link or links exert a force component to the pulley flange which either adds to or subtracts from the force applied to the flange by other means.